Heat pumps are devices that is capable of producing hot water with a high temperature using a heat source with a low temperature. In general, heat pumps produce hot water with a set temperature and a set flow rate using a heat source that is introduced with a predetermined temperature and a predetermined flow rate.
In a new renewable heat source, such as a geothermal heat source, a sewage heat source, a solar heat source, and a river water heat source, the temperature of the heat source is not constant, and flow rate (or heat flow) characteristics change significantly. In addition, in reality, a demand source that uses hot water requires hot water with various levels of temperature depending on the purpose of demand. However, there are limitations in satisfying characteristics of the heat source and characteristics of the demand source using general heat pumps.
Korean Patent Registration No. 0780281 discloses a technique for supplying hot water to a demand source by operating a heat pump using fresh water, river water, and the like. However, in such a technique, a plurality of heat pumps are simply installed in parallel and operate. It is difficult to efficiently use heat sources with various levels of temperature and to meet the requirement of a demand source that requires hot water with various levels of temperature.